do not return a const file and add localFile helper

python/core/qgsnetworkcontentfetcherregistry.sip.in

@@ -120,6 +120,8 @@ Create the registry for temporary downloaded files
    If the download starts immediately, it will not redownload any already fetched or currently fetching file.
 %End
 
+    QString localPath( const QString &filePathOrUrl );
+
 };
 
 /************************************************************************

src/core/qgsnetworkcontentfetcherregistry.cpp

@@ -101,5 +101,32 @@ const QgsFetchedContent *QgsNetworkContentFetcherRegistry::fetch( const QUrl &ur
   return content;
 }
 
+QString QgsNetworkContentFetcherRegistry::localPath( const QString &filePathOrUrl )
+{
+  QString path = filePathOrUrl;
+
+  if ( !QUrl::fromUserInput( filePathOrUrl ).isLocalFile() )
+  {
+    if ( mFileRegistry.contains( QUrl( path ) ) )
+    {
+      const QgsFetchedContent *content = mFileRegistry.value( QUrl( path ) );
+      if ( content->status() == QgsFetchedContent::Finished && !content->filePath().isEmpty() )
+      {
+        path = content->filePath();
+      }
+      else
+      {
+        // if the file is not downloaded yet or has failed, return empty string
+        path = QStringLiteral();
+      }
+    }
+    else
+    {
+      // if registry doesn't contain the URL, keep path unchanged
+    }
+  }
+  return path;
+}
+
 
 

src/core/qgsnetworkcontentfetcherregistry.h

@@ -59,7 +59,7 @@ class CORE_EXPORT QgsFetchedContent : public QObject
 
 #ifndef SIP_RUN
     //! Return a pointer to the local file, a null pointer if the file is not accessible yet.
-    const QFile *file() const {return mFile;}
+    QFile *file() const {return mFile;}
 #endif
 
     //! Return the path to the local file, an empty string if the file is not accessible yet.
@@ -139,6 +139,8 @@ class CORE_EXPORT QgsNetworkContentFetcherRegistry : public QObject
      */
     const QgsFetchedContent *fetch( const QUrl &url, const FetchingMode &fetchingMode = DownloadLater );
 
+    QString localPath( const QString &filePathOrUrl );
+
   private:
     QMap<QUrl, QgsFetchedContent *> mFileRegistry;
 

tests/src/python/test_qgsnetworkcontentfetcherregistry.py

@@ -70,8 +70,9 @@ class TestQgsNetworkContentFetcherTask(unittest.TestCase):
             app.processEvents()
 
     def testFetchGoodUrl(self):
+        url = 'http://localhost:' + str(self.port) + '/qgis_local_server/index.html'
         registry = QgsApplication.networkContentFetcherRegistry()
-        content = registry.fetch(QUrl('http://localhost:' + str(self.port) + '/qgis_local_server/index.html'))
+        content = registry.fetch(QUrl(url))
         self.loaded = False
 
         def check_reply():
@@ -85,8 +86,10 @@ class TestQgsNetworkContentFetcherTask(unittest.TestCase):
         while not self.loaded:
             app.processEvents()
 
+        self.assertEqual(registry.localPath(url), content.filePath())
+
         # create new content with same URL
-        contentV2 = registry.fetch(QUrl('http://localhost:' + str(self.port) + '/qgis_local_server/index.html'))
+        contentV2 = registry.fetch(QUrl(url))
         self.assertEqual(contentV2.status(), QgsFetchedContent.Finished)
 
     def testFetchReloadUrl(self):
@@ -124,6 +127,18 @@ class TestQgsNetworkContentFetcherTask(unittest.TestCase):
 
         os.remove('qgis_local_server/simple_content.txt')
 
+    def testLocalPath(self):
+        registry = QgsApplication.networkContentFetcherRegistry()
+        filePath = 'qgis_local_server/index.html'
+        self.assertEqual(registry.localPath(filePath), filePath)
+
+        # a non existent download shall return untouched the path
+        self.assertEqual(registry.localPath('xxxx'), 'xxxx')
+
+        # an existent but unfinished download should return an empty path
+        content = registry.fetch(QUrl('xxxx'))
+        self.assertEqual(registry.localPath('xxxx'), '')
+
 
 if __name__ == "__main__":
     unittest.main()